DE-PS 39 11 496 describes a generic valve drive of the pre-cited type. In this valve drive, the height of the closing spring can be varied through an eccentric. The variation of the height of the closing spring is intended to vary its resilient force so that the opening period of the gas exchange valve can be influenced.
However, a person of ordinary skill in the art finds no suggestion in the aforesaid document as to how disturbances that can have a negative influence on the oscillatory spring-mass system can be excluded in a simple manner. Such disturbances are mainly gas forces acting on the gas exchange valve and an increasing impact on the valve seat with increasing running time of the internal combustion engine. Installation tolerances can constitute additional disturbances. These can arise, for example, from differing lengths of the springs used but attention must also be paid to differing spring constants. In the most unfavorable case, these disturbances can lead to inoperatability of the oscillatory spring-mass system because the armature can no longer be excited out of its idle position to effect a complete oscillation between its end positions.